PSI - Issue 44

Diego Alejandro Talledo et al. / Procedia Structural Integrity 44 (2023) 918–925 Talledo et al. / Structural Integrity Procedia 00 (2022) 000–000

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law, assuming a linear elastic behavior with stiffness equal to the shear deformability up to the shear strength of the panel, followed by a linear softening branch. For each capacity curve obtained by the pushover analyses, the N2 procedure (Fajfar 1996) is carried out and the Peak Ground Acceleration, as well as the return period of the earthquake, corresponding to the spectrum for which the target point is equal to the structural capacity, is evaluated with respect to both Life Safety (LSLS) and Damage Limitation (DLLS) Limit States (    ,   ,   and    ,   , ).

Fig. 2. FE models: (a) existing RC building; (b) retrofitted building with bare RC-framed skin; (c) retrofitted building with RC-framed skin.

4.1. Nonlinear static analysis for the existing RC frame building and for the retrofitted building Fig. 3 shows the capacity curves in X- and Y- directions obtained by the pushover analysis for the existing building, adopting a modal and a proportional to the masses (uniform) distribution of horizontal forces. The attainment of the ultimate chord rotation is highlighted with a yellow circle, and the brittle shear failure with a green triangle. In both cases, a label indicates if the failure element is a beam, ‘B’, or a column ‘C’. Finally, the attainment of drift equal to 5 ‰ is indicated with an orange circle. The bi-linearized curves are also reported with a thicker line.

(a) (b) Fig. 3. Capacity curves and bi-linearization procedure for existing RC building: (a) X-direction; and (b) Y-direction. As expected, the pushover curve of the existing building in the Y-direction is characterized by strong deformability associated with a lower strength (about one half) compared to the response in the X-direction (i.e., the strong direction). However, despite the apparent ductility of the capacity curve, in Y-direction the structure is subjected to a brittle shear failure occurring on the flat beams, while in X-direction the failure is due to the attainment of the limit chord rotation in two central columns of the ground floor. Therefore, the existing building exhibits a remarkably different behavior in the two main directions. Fig. 4 and Fig. 5 show the capacity curves for the existing building retrofitted with the RC-framed skin with columns sections of 250 mm x 250 mm, by considering or not the external reinforced plaster. The adoption of the proposed retrofitting technology, both with and without the external reinforced plaster, regularizes the response of the building in the two directions and in all cases, the failure is achieved for the attainment of the limit chord rotation in a column of the existing building, with a peak strength around 2500 kN (see Fig. 4), about 4 times greater than that of